PETROGRAPHY, GAMMA RADIATION MEASUREMENTS AND DOSE RATE, NORTHEASTERN UM ARA AREA, SOUTH EASTERN DESERT, EGYPT

The northern part of Um Ara alkali feldspar microgranite has subjected to extensive post-magmatic
metasomatic reworking resulting in development of amazonitized and albitized zones, reflecting K- and Na
metasomatism leading to gross enrichment in U and Th towards the more evolved phases (e.g., albitized
zones). Spectrometric survey data indicate that eU in Dokhan volcanics has the range of 2 to 42 ppm with
an average value of 10 ppm and in monzogranites. It varies from 3 to 13 ppm with an average of 7 ppm
while in alkali feldspar microgranites eU contents vary from 3 to 282 ppm with an average value of 30 ppm.
The (eTh) contents in Dokhan volcanics ranges from 5-51 ppm with an average 18 ppm, in monzogranites
their content was in the range of 11 to 47 ppm with an average value of 27 ppm where it ranges from 14
to 83 ppm with an average 46 ppm in alkali feldspar granite. The enhanced uranium content in altered
zones was attributed to disseminated and fracture filling uranophane, autonite, in addition to other U and
Th bearing minerals (such as columbite, zircon, monazite, xenotime and fluorite). Gamma-radiation dose
rate and annual effective dose equivalents in mSv/y, Radium equivalent activity, external (Hex) and internal
hazard index (Hin) and gamma activity index (I) for all investigated samples were calculated to assess the
potential radiation hazard for people living in dwellings made of the studied granites. Alkali feldspar granite
activities would suggest that caution must be taken when using granites as building materials because they
have radioactivity above the proposed acceptable level.